Electron gun of the ion trap type



1955 R. B. GETHMANN ELECTRON GUN OF THE ION TRAP TYPE Filed March 18, 1953 Inventor:

Richard B. Gethmann y M His At'b or-ney.

- 6 p F Ice Patented Nov. 8, 1955 ELECTRON GUN OF THE ION TRAP TYPE Richard Barton Gethmann, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application March 18, 1953, Serial No. 343,195

16 Claims. (Cl. 313-79) The present invention relates to an improved ion trap type electron gun, and particularly, to an improved mag netic deflecting structure therefor.

It is generally understood that ions as well as electrons are present in the electric beam of high vacuum cathode ray tubes of the type commonly used in television receivers. The presence of negative ions tends to result in screen burning, particularly in magnetic deflection type tubes, since in these tubes the ions are substantially undeflected and continuously impinge on a small area near the center of the tube. Many television picture tubes have been manufactured which utilize the selective deflection of ions and electrons by a combination of electric and magnetic fields to collect the ions on a suitable part of the gun structure While allowing the electrons of the beam to travel on toward the screen of the tube. This type of ion trapping is readily possible since both ions and electrons are deflected to the same extent by an electrostatic field, while the ions are deflected to a much less extent by a magnetic field than are the electrons. Prior art structures have, in some cases, provided a component of electrostatic field transverse to the beam direction by shaping adjacent electrodes of the gun structure. A magnetic field for producing a deflecting force in the opposite direction has been provided by magnetic means external to the tube. While these devices have, in general, been acceptable, the high reluctance of the magnetic circuit through the neck of the tube from one side to the other has required rather substantial sources of magnetic potential to produce the desired field. These devices being independent of the gun structure as far as their physical mounting is concerned have caused considerable trouble from the standpoint of obtaining and maintaining accurate position of the magnetic structure with respect to the gun. This problem exists, not only during manufacture of the sets but during the life of the set, and particularly at times of maintenance of the set such as replacement of the picture tube.

In accordance with an important aspect of the present invention, I provide a magnetic deflection structure within the tube, and preferably forming a part of the gun structure, for giving a transverse deflection to the electrons, and particularly to function in combination with an opposed electrostatic field to provide an ion trap.

It is also an object of my invention to provide an ion trap type of gun which minimizes problems of focusing which usually are created by gun structures of this type.

It is a still further object of the invention to overcome the above-listed disadvantages of the prior art ion trap. structures and, at the same time, to provide a structure which is readily manufactured by mass production methods.

Further objects and advantages of my invention will become apparent as the following description proceeds,-

electron gun embodying my invention; and

Fig. 2 is a sectional view taken along the line 2-2 0 Fig. 1.

Referring now to the drawing, I have shown my invention embodied in a tetrode type of electron gun including a cathode sleeve 1 having on the end wall thereof an emissive coating 2 supported in insulated relation within a cupshaped control member or grid 3 having a beam passage 4 centrally located in the end wall thereof. In addition to the control grid cathode assembly, the gun includes an accelerating electrode or number two grid 5 and an anode 6. In the embodiment illustrated, a magnetic focusing assembly designated generally by the numeral 7 is supported on the outer end of the anode 6. Said magnetic focusing structure is of the type described and claimed in my copending application Serial No. 274,785, filed March 4, 1952, and assigned to the assignee of this application and on which U. S. Patent No. 2,681,421 was granted June 15, 1954.

The focusing structure includes a pair of annular pole pieces 8 and 9 between which are supported a plurality of cylindrical permanent magnets 10 to produce a magneto motive force across a focusing or lens member 11 having a central passage therethrough. As illustrated, the lens member ii is supported within a cylindrical member 12 forming an extension of the anode 6. The various electrodes of the gun assembly are supported in the usual manner by means of studs 13 welded to the electrodes and embedded in a glass rod or stalk 14. As illustrated the focusing structure is in axial alignment with the neck of the cathode ray tube a portion of which is illustrated in the drawing at 15. In accordance with usual practice the anode 6 is maintained at the desired potential as a result of its connection with a conducting coating 16 on the wall of the tube. Contact is established through flexible contact members 17. For reasons that will become more apparent at a later point in the specification the remainder of the gun structure extends at a slight angle with respect to the focusing structure and also at a slight angle with respect to the neck of the cathode ray tube.

In the particular embodiment of my invention'illustrated in the drawing the magnetic structure for effecting the transverse deflection of the electrons for ion trapping purposes is in the form of a sub-assembly which is supported within' the cylindrical anode electrode 6. As clearly illustrated in Figs. 1 and 2 of the drawing the sub-assembly includes a generally cup shaped member 18 having a wall portion 19 adjacent the open'end thereof conforming in size and shape to the interior of the anode cylinder 6. The cup is drawn in somewhat near the closed end and shaped to position and support the magnetic field producing assembly including a pair of elongated pole pieces 20 and 21 as illustrated. The cup is drawn in such a manner as to provide shoulders 22, 23, 24 and 25 which prevent the pole pieces from spreading outwardly. A portion of the side wall of the cup 26 is struck inwardlly between the pole pieces at one end thereof to prevent the pole pieces from moving together. At the opposite end the'pole pieces are held apart by a cylindrical permanent magnet 27 which provides the magneto motive force for the assembly. As illustrated, the pole pieces are suitably recessed to receive the ends of the permanent magnet; The assembly including the pole pieces 20 and 21 and the permanent magnet 27 are held in position and against the closed end of the cup by spot welding the ends of the pole piece to the flattened areas of the cupdesignated by the numeral 28. The closed end of the cup is provided with a beam limiting aperture 29 which is centrally located in a direction transverse to the elongated pole -pieces 'but is substantially off center with respect to the anode sures the uniform spacing of the pole pieces 20 and 21 necessary to produce a uniform magnetic field. The pole pieces 20 and 21 are also shaped to eliminate strong concentrations of the flux such as would occur at sharp edges. As illustrated the opposed surfaces are suitably curved and may be cylindrical surfaces.

In order that the beam limiting aperture 29 shall be in a substantially field free region, the lower end of the anode cylinder 6 is provided with a diaphragm 3G having a beam aperture 31 formed therein and defined by a curved wall. The closed end of the cup including the limiting aperture 29 is preferably positioned away from the diaphragm 30 by a distance at least equal to the diameter of the aperture 31 in order to insure that the beam limiting aperture 29 is in a substantially field free region.

While the operation of the device just described is believed to be apparent to those skilled in the art from the foregoing detailed description it is believed well to briefly trace the action of the ion trap on an electric beam including ions and electrons. The beam originating at the cathode surface 2 passes through the apertures in the control and accelerating grids 3 and 5 and travels on the axis of these electrodes. As the composite beam traverses the space between the accelerating grid 5 and the anode 6, it is subjected to a transverse component of electric field tending to deflect the entire beam to the right as viewed in Fig. 1. In the normal application of electron guns of the type here described the accelerating grid is operated at a voltage in the order of 400 volts and the final anode voltage is in the order of 12 to 16 kilovolts. The composite beam having been deflected to the right moves substantially from the axis of the electrode 6 and passes through the limiting aperture 29 of the magnetic deflecting structure. As the beam passes through the space between the pole pieces 20 and 21 it is subjected to a magnetic field tending to deflect the beam to the left. The strength of the magnetic field is just sufflcient to return the electrons to the axis of the focusing structure 7, the ions, being substantially undeflected, continue on and are collected on an interior surface of anode 6.

The desired strength of the magnet is obtained by effecting its magnetization after the gun has been asembled in a cathode ray tube. On final test, magnet 27 is magnetized to such a value that it is masked out by the focusing structure on opposite sides by adjusting the anode voltage to values which are equally above and below normal operating voltage. For example, if a tube has a normal anode voltage of 14,000 volts, the spot will be masked out on opposite sides of the center at anode voltages of 9,000 volts and 19,000 volts.

It is also apparent at this point why the focusing structure is on the axis of the tube envelope while the axis of the remainder of the gun structure extends to the left of the axis of the tube envelope. As the beam passes through the accelerating electrode 5 it is to the left of the axis of the envelope and the focusing structure. When it is deflected to the right in the region between the accelerating electrode 5 and the anode 6 it moves toward the axis of the tube envelope. It is possible under these circumstances for a single magnetic deflection to bend the beam of electrons just sufliciently to coincide with the axis of the tube envelope and the focusing structure. If the lower part of the gun structure were on the tube axis and were deflected to the right of that axis by the electrostatic field then it would tend to cross the axis of the tube envelope when deflected in the opposite direction by the magnetic field produced between the pole pieces 20 and 21.

While I have shown and described my invention applied to an electron gun in which the electrostatic field is provided by shaping the adjacent electrodes of the gun, it will be apparent that in its broader aspects it is applicable to other gun structures where the transverse electrostatic field for example, may be provided by means external to the gun structure. It will also be apparent that the magnetic deflecting structure need not be placed at a later point along the beam path than the electrostatic deflection. While it is generally understood by those skilled in the art that the sheet metal parts of the gun structure such as grids 2 and 5, and anode 6, the cup 18 and the diaphragm 30 are formed of non-magnetic material, it should be mentioned here so that there will be no misunderstanding as to the operation of the device. Such materials commonly used include stainless steel and certain copper nickel alloys.

While I have described a particular embodiment of my invention it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An ion trap type of electron gun comprising means providing an electric beam having a given direction and including ions and electrons, means subjecting the beam to an electrostatic field transverse to said direction tending to deflect both said ions and electrons from said direction, and means within said gun including a permanent magnet and a pair of pole pieces subjecting said beam to a transverse magnetic field tending to deflect said electrons toward said original direction.

2. An electric discharge device comprising means providing an electric beam having a given direction and including ions and electrons, means subjecting the beam to an electrostatic field transverse to said direction tending to deflect both said ions and electrons from said direction, a cylindrical accelerating electrode in the path of said beam, and means including a permanent magnet and a pair of pole pieces within said electrode subjecting said beam to a transverse magnetic field tending to deflect said electrons toward said original direction.

3. An electric discharge device comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode in the path of said beam, and means including a permanent magnet and a pair of pole pieces within said electrode subjecting said beam to a transverse magnetic field.

4. An ion trap type of electron gun comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode in the path of said beam and a magnetic deflecting structure within said electrode including a pair of elongated pole pieces extending in generally parallel relation on opposite sides of the beam path and permanent magnet means extending between said pole pieces.

5. An ion trap type of electron gun comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode in the path of said beam and a magnetic deflecting structure within said electrode including a pair of elongated pole pieces extending in generally parallel relation on opposite sides of the beam path, said pole pieces having curved surfaces in the direction of beam travel and permanent magnet means extending between said pole pieces.

6. An electron gun comprising means providing an electron beam, a hollow cylindrical electrode in the path of said beam, a magnetic structure within said electrode for producing a transverse deflection of electrons within said electrode, and a magnetic focusing structure supported from the end of said electrode and having a focusing passage therethrough.

7. An electron gun comprising means providing an electron beam, a hollow cylindrical electrode in the path of said beam, a magnetic structure within said electrode for producing a transverse deflection of electrons within said electrode, and a magnetic focusing structure supported from the end of said electrode and having a focusing passage therethrough, the axis of said focusing structure extending at an angle to the axis of said electrode.

8. An ion trap type of electron gun comprising means producing an electric beam having a given direction and including ions and electrons, said gun including a pair of cylindrical electrodes supported in insulated relation and spaced in said direction, and said electrodes being shaped to deflect both said ions and said electrons transverse to said direction and a magnetic deflecting structure within one of said electrodes for deflecting the electrons of said beam in a direction opposite to the deflection produced by said electrodes, said structure including a cup-like cylindrical member having a limiting aperture in the closed end thereof, a permanent magnet extending transversely of the axis of said cup-like member and a pair of pole pieces extending from the ends of said magnet and positioned on opposite sides of said aperture, and a magnetic focusing structure supported on the end of said one electrode and having a passage therethrough at an angle to the axis of said one electrode.

9. An ion trap type of electron gun comprising means producing an electric beam having a given direction and including ions and electrons, said gun including a pair of cylindrical electrodes supported in insulated relation and spaced in said direction, a magnetic deflecting structure within one of said electrodes for deflecting the electrons of said beam transversely with respect to the beam path, said structure including a transverse member having a limiting aperture therein, a permanent magnet extending transversely of the axis of said one electrode, a pair of pole pieces extending from the ends of said magnet and positioned on opposite sides of said aperture, and an apertured member at the end of said electrode to provide a substantially field-free region at said limiting aperture.

10. An ion trap type of electron gun comprising means producing an electric beam having a given direction and including ions and electrons, said gun including a pair of cylindrical electrodes supported in insulated relation and spaced in said direction, a magnetic deflecting structure within one of said electrodes for deflecting the electrons of said beam transversely with respect to the beam path, said structure including a transverse member having a limiting aperture therein, a permanent magnet extending transversely of the axis of said one electrode, and a pair of pole pieces extending from the ends of said magnet and positioned on opposite sides of said aperture.

11. A magnetic deflecting structure comprising a cuplike sheet metal member of non-magnetic material having an aperture in the end wall thereof, a pair of elongated pole pieces extending transversely within said cup on opposite sides of said aperture, a permanent magnet extending between said pole pieces near one end thereof,

a portion of the side wall of said cup extending between the opposite ends of said pole pieces, said cup being shaped to provide shoulders engaging the outer surfaces of said pole pieces at the ends thereof and flattened surfaces engaging the ends of said pole pieces to facilitate Welding of said pole pieces to said cup.

12. A magnetic deflecting structure comprising a cuplike sheet metal member of non-magnetic material having an aperture in the end wall thereof, a pair of elongated pole pieces extending transversely within said cup on opposite sides of said aperture, a permanent magnet extending between said pole pieces near one end thereof and having the ends thereof received in recesses formed in said pole pieces.

13. A magnetic beam deflecting structure comprising a cup-like sheet metal member having an aperture in the end wall thereof, a pair of elongated pole pieces extending transversely within said cup on opposite sides of said aperture, and a permanent magnet extending between said pole pieces near one end thereof.

14. An electric discharge device comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode in the path of said beam and means including a permanent magnet and a pair of pole pieces supported from said electrode subjecting said beam to a transverse magnetic field.

15. An electric discharge device comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode having a beam passage therethrough and means supported from said electrode subjecting said beam to a transverse magnetic field including a permanent magnet and a pair of pole pieces, said pole pieces extending on opposite sides of said beam passage.

16. An electric discharge device comprising means providing an electric beam having a given direction and including ions and electrons, a hollow cylindrical electrode having a beam passage therethrough and means supported from said electrode subjecting said beam to a transverse magnetic field including a permanent magnet and a pair of elongated pole pieces, said pole pieces extending on opposite sides of said beam passage and having the opposed faces thereof curved about axes parallel to the length of said pole pieces.

References Cited in the file of this patent UNITED STATES PATENTS 2,188,579 Schlesinger Jan. 30, 1940 2,305,761 Borries et al. Dec. 22, 1942 2,496,127 Kelar Jan. 31, 1950 2,515,305 Kelar July 18, 1950 2,619,607 Steers Nov. 25, 1952 

